Understand the concept of conjugate acids and bases: A conjugate acid is formed when a base gains a proton (H⁺). Conversely, a conjugate base is formed when an acid loses a proton.
Identify the base in the problem: The base given is \( \text{PO}_4^{3-} \).
Determine the process to find the conjugate acid: To find the conjugate acid, add a proton (H⁺) to the base \( \text{PO}_4^{3-} \).
Perform the addition of a proton: Adding a proton to \( \text{PO}_4^{3-} \) results in \( \text{HPO}_4^{2-} \). This is because the addition of a proton increases the charge by +1, changing the charge from -3 to -2.
Verify the result: Check that \( \text{HPO}_4^{2-} \) is indeed the conjugate acid of \( \text{PO}_4^{3-} \) by confirming that it has one more hydrogen atom and a charge that is one unit less negative.